1. Field of the Invention
This invention relates to automatic dishwasher detergent compositions containing low-foaming nonionic surfactants.
2. Description of the Prior Art
Detergent compositions containing, in combination, alkaline salts such as sodium silicate and sodium carbonate, an alkaline polyphosphate such as sodium tripolyphosphate, a low-foaming, chlorine-compatible nonionic surfactant, and a chlorine containing compound that provides a hydrochorite ion in solution are well known and have particular utility in machine dishwashing.
There are many different views on how dishwashing detergents function, but there seems to be general agreement on several points, to wit: 1. The main cleaning is done by the alkaline salts whether by emulsification, saponification, sequestering hard water ions and/or other mechanisms; 2. The active chlorine compound is aimed principally at protein soil but also serves as a destainer and germicide; 3. solubilized protein soil is a main cause of foaming problems; and 4. the surfactant provides optimum cleaning and good spotting and filming results while also providing defoaming power in the presence of foam producing food soil, but the use of auxiliary foam depressants is generally preferred to achieve optimum foam suppressing characteristics. Thus, while dishwasher detergents may clean by a number of processes, the combination of requirements for surfactants that are employed in such detergent compositions are well established. The surfactant must be low foaming and be capable of defoaming food soils; it must have a low cloud point (generally less than about 30.degree. C.) so that it can function as a foam suppressor by separating from solution under hot water temperature (e.g. about 60.degree. C.) but at the same time be sufficiently soluble in the wash liquor to provide wetting; it must be compatible with active chlorine and not markedly decompose those chlorinated compounds used in detergent compositions; and it must have good wetting characteristics to give good spotting and filming results.
A wide variety of nonionic surfactants have been disclosed as useful in automatic dishwasher detergent compositions. Broad disclosures of block oxypropylene/oxyethylene adducts of alcohols have been described, for example, in U.S. Pat. No. 3,314,891 (Schmolka et al.) and U.S. Pat. No. 4,272,394 (Kaneko). These patents, however, do not disclose the particular nonionic surfactant structures claimed in the present invention. In contrast, the prior art contains disclosures, such as in U.S. Pat. No. 2,903,486 (Brown et al.), suggesting that oxyalkylene adducts of alkylphenols having block oxypropylene/oxyethylene groups with the oxypropylene groups proximate to the alkylphenoxylate would be undesirable.
A specific nonionic surfactant structure useful in the automatic dishwasher detergent composition of the present invention, has been disclosed in U.S. Pat. No. 4,252,528 (Decker et al.). This patent, however, relates to lubricant compositions for finishing synthetic fibers.